e1-e2 (cfa) concept of packet switching for internal ... switching and...آ  virtual circuit packet...

Download E1-E2 (CFA) CONCEPT OF PACKET SWITCHING For internal ... Switching and...آ  VIRTUAL CIRCUIT PACKET SWITCHING

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  • CONCEPTCONCEPT

    OF OF

    E1-E2 (CFA)

    1For internal circulation of BSNL only

    OF OF

    PACKET SWITCHINGPACKET SWITCHING

    Date of creation:-19/03/2011

  • INTRODUCTION

    � Packet-switched and circuit-switched networks use two

    different technologies for sending messages and data from

    one point to another.

    � Each have their advantages and disadvantages too.

    2

    � There is another technology almost not in use called the

    Message switched network best known by the descriptive

    term store and forward.

    For internal circulation of BSNL onlyDate of creation:-19/03/2011

  • CIRCUIT SWITCHING

    � Circuit switching was designed in 1878 in order to send

    telephone calls down a dedicated channel. This channel

    remained open and in use throughout the whole call and

    could not be used by any other data or phone calls.

    � There are three phases in circuit switching:

    3For internal circulation of BSNL only

    � There are three phases in circuit switching:

    Establish

    Transfer

    Disconnect

    Date of creation:-19/03/2011

  • CIRCUIT SWITCHING

    � The telephone message is sent in one go, it is not broken

    up. The message arrives in the same order that it was

    originally sent.

    � In modern circuit-switched networks, electronic signals pass

    through several switches before a connection is established.

    4

    through several switches before a connection is established.

    � During a call, no other network traffic can use those

    switches.

    � The resources remain dedicated to the circuit during the

    entire data transfer and the entire message follows the same

    path.

    For internal circulation of BSNL onlyDate of creation:-19/03/2011

  • CIRCUIT SWITCHING

    � Circuit switching can be analogue or digital

    �With the expanded use of the Internet for voice and

    video, analysts predict a gradual shift away from circuit-

    switched networks.

    5

    � A circuit-switched network is excellent for data that

    needs a constant link from end-to-end. For example real-

    time video.

    For internal circulation of BSNL onlyDate of creation:-19/03/2011

  • CIRCUIT SWITCHING

    � Circuit Switching

    �Advantages:

    �Circuit is dedicated to the call – no interference,

    no sharing

    �Guaranteed the full bandwidth for the duration of

    the call

    �Guaranteed Quality of Service

    For internal circulation of BSNL onlyDate of creation:-19/03/2011 6

  • CIRCUIT SWITCHING

    � Disadvantages:

    �Inefficient – the equipment may be unused for a lot

    of the call, if no data is being sent, the dedicated

    line still remains open

    �Takes a relatively long time to set up the circuit

    7

    �During a crisis or disaster, the network may

    become unstable or unavailable.

    �It was primarily developed for voice traffic rather

    than data traffic.

    For internal circulation of BSNL onlyDate of creation:-19/03/2011

  • CIRCUIT SWITCHING(ILLUSTRATION)

    8For internal circulation of BSNL only Date of creation:-19/03/2011

  • CIRCUIT SWITCHING(ILLUSTRATION)

    9For internal circulation of BSNL only Date of creation:-19/03/2011

  • PACKET SWITCHING

    � In packet-based networks, the message gets broken

    into small data packets. These packet travel around the

    network seeking out the most efficient route to travel as

    circuits become available. This does not necessarily

    10

    mean that they seek out the shortest route.

    � Each packet may go a different route from the others.

    � Each packet is sent with a ‘header address’. This tells it

    where its final destination is, so it knows where to go.

    For internal circulation of BSNL onlyDate of creation:-19/03/2011

  • PACKET SWITCHING

    • The header address also describes the sequence for

    reassembly at the destination computer so that the

    packets are put back into the correct order.

    • One packet also contains details of how many packets

    should be arriving so that the recipient computer knows if

    11

    should be arriving so that the recipient computer knows if

    one packet has failed to turn up.

    • If a packet fails to arrive, the recipient computer sends a

    message back to the computer which originally sent the

    data, asking for the missing packet to be resent.

    For internal circulation of BSNL onlyDate of creation:-19/03/2011

  • PACKET SWITCHING

    �Advantages:

    �Security

    �Bandwidth used to full potential

    �Devices of different speeds can communicate

    �Not affected by line failure (re diverts signal)

    12

    �Availability – do not have to wait for a direct

    connection to become available

    �During a crisis or disaster, when the public telephone

    network might stop working, e-mails and texts can still

    be sent via packet switching

    For internal circulation of BSNL onlyDate of creation:-19/03/2011

  • PACKET SWITCHING

    �Disadvantages

    �Under heavy use there can be a delay

    �Data packets can get lost or become corrupted

    �Protocols are needed for a reliable transfer

    13

    �Not so good for some types data streams e.g real-

    time video streams can lose frames due to the way

    packets arrive out of sequence.

    For internal circulation of BSNL onlyDate of creation:-19/03/2011

  • PACKET SWITCHING

    � SWITCHING TECHNIQUE

    � Station breaks long message into packets

    � Packets sent one at a time to the network

    � Packets are handled in two way

    14

    � Datagram

    � Virtual circuit

    For internal circulation of BSNL onlyDate of creation:-19/03/2011

  • DATAGRAM PACKET SWITCHING � In datagram approach each packet is treated independently

    with no reference to packets that have gone before. No

    connection is set up.

    � Packets can take any practical route

    � Packets may arrive out of order

    15

    � Packets may go missing

    � Up to receiver to re-order packets and recover from missing

    packets

    �More processing time per packet per node

    � Robust in the face of link or node failures.

    For internal circulation of BSNL onlyDate of creation:-19/03/2011

  • DATAGRAM PACKET SWITCHING

    Datagram

    Approach

    16For internal circulation of BSNL only Date of creation:-19/03/2011

  • DATAGRAM PACKET SWITCHING

    • The approach seems to be feasible, but we have not

    considered a very important aspect, updation of routing

    tables. If a new node is added to the sub-network, all the

    routing tables at various nodes need to be updated.

    17

    • In heavy traffic conditions, datagram movement across the

    sub-network can stop altogether.

    • The main implementation of Datagram Switching network

    is the Internet which uses the IP network protocol.

    Date of creation:-19/03/2011 For internal circulation of BSNL only

  • VIRTUAL CIRCUIT PACKET SWITCHING

    � In the Virtual Circuit approach a pre-planned route is

    established before any packets are sent.

    � There is a call set up before the exchange of data

    (handshake).

    � All packets follow the same route and therefore arrive in

    sequence.

    18

    sequence.

    � Each packet contains a virtual circuit identifier instead of

    destination address

    �More set up time

    � No routing decisions required for each packet - Less

    routing or processing time

    Date of creation:-19/03/2011 For internal circulation of BSNL only

  • VIRTUAL CIRCUIT PACKET SWITCHING

    � Susceptible to data loss in the face of link or node failure

    � Clear request to drop circuit

    � Not a dedicated path

    � The most common forms of Virtual Circuit networks are

    19

    � The most common forms of Virtual Circuit networks are

    X.25 and Frame Relay, which are commonly used for

    public data networks (PDN)

    Date of creation:-19/03/2011 For internal circulation of BSNL only

  • VIRTUAL CIRCUIT PACKET SWITCHING

    Virtual Circuit Approach

    20 Date of creation:-19/03/2011 For internal circulation of BSNL only

  • VIRTUAL CIRCUIT PACKET SWITCHING

    Source-to-destination data transfer

    21 Date of creation:-19/03/2011 For internal circulation of BSNL only

  • VIRTUAL CIRCUIT PACKET SWITCHING

    � Virtual circuits can be either permanent, called Permanent

    virtual Circuits (PVC), or temporary, called Switched Virtual

    Circuits (SVCs).

    � A Permanent Virtual Circuit (PVC) is a virtual circuit that is

    permanently available to the user.

    22

    � A PVC is defined in advance by a network manager.

    � If permanent, a

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